About the domain relationship for replication
For a target: the relationship between the originating domain and the target domain or domains is established in the originating domain. Specifically, by configuring the target storage server in the Replication tab of the Change Storage Server dialog box of the source storage server.
See Configuring a target for MSDP replication to a remote domain.
Before you configure the replication relationship, you can add the target master server as a trusted host.
See About trusted primary servers for Auto Image Replication.
Caution:
Choose the target storage server carefully. A target storage server must not also be a storage server for the originating domain.